Songbirds’ spring plumage is colorful by design

Timothy Hill

Beautiful bird plumage these days matches the color pallet of wildflowers — cardinals as red as Indian paintbrushes, andbluebirds as blue as bluebonnets.

It’s not happenstance. Wildflowers attract insects that provide nourishment for birds to sustain themselves and nourish newborn chicks.

Several species of birds eat certain plant fruits and later excrete the seeds across the landscape, and seeds land on the ground conveniently fertilized with bird poop.  

But to understand the beautiful spring colors on songbirds, we first need to understand autumn molt, when the birds undergo a complete change of feathers. The new coat of feathers has dull tones and especially dull tips, giving the birds a lackluster winter appearance.  

Spring plumage on songbirds results from a combination of factors, including the months-long abrasion of dull winter feather tips to reveal the radiant color underneath.

For example, cardinals have gray edges on their basic plumage during winter. But the edges wear off by spring to reveal pigmented breeding plumage, which gives the male a fire engine red color. Likewise, the feather tips of basic plumaged American robins wear away by spring to show pigmented brick-red feathers on the underside.

Feathers keep birds warm, cool, and dry.  
Fully formed feathers are highly complex structures comprised of a feather shaft holding feather vanes of intricately woven barbs and barbules that hold the feather together as a tightly knit structure.
The five major feathers are flight feathers on the wings, covert feathers overlapping the wing feathers, tail feathers, contour feathers covering the body, and insulating down feathers underneath the contour feathers.   
Most songbirds born in the spring shed natal plumage during late summer or early autumn for their first set of adult feathers. 
Birds such as gulls and eagles go through several years of molt to reach adult plumage.  

Other factors creating colorful plumage involve feather structures that refract light and hormonal changes induced by increased daylight hours with the approach of spring.

A few birds undergo a second feather molt in spring, changing their color. For example, American goldfinches will molt all their feathers into brownish-gray plumage for the winter but will undergo another spring molt of body feathers, not wing feathers. That explains their remarkable change into canary-like yellow plumage that matches the yellow in a field of sunflowers where they feed on northern breeding grounds.  

Transitions to spring plumage patterns are complex, depending on a bird’s age, gender, feather structure, and degree of color pigmentation. Yet male songbirds are generally brighter in spring than females because the male color is a factor in luring mates. Females have a dull color to conceal themselves when brooding eggs in nests.

Here’s a surprise: The bright blue on male eastern bluebirds and on blue jays does not derive from pigmentation. Instead, the complex structure of keratin proteins in their feathers reflects blue wavelengths. And by spring, the reflection of blue wavelengths becomes brighter.  

Email Gary Clark at [email protected]. Book of Texas Birds, by Gary Clark with photography by Kathy Adams Clark (Texas A&M University Press.)


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